Vascular diseases, and complications arising from vascular diseases, are a leading cause of death in modern society. Medical science therefore, is increasingly concerned with the diagnosis and treatment of these types of diseases. Recently many new techniques have been developed in this area.
As an example, angioplasty is a medical procedure in which an inflatable balloon is used to widen a narrowed or stenotic segment of an artery. As another example, atherectomy is a medical procedure in which plaque in an obstructed artery is cut away and removed from the artery.
FIGS. 1A, 2A and 3A illustrate some different arterial conditions that may occur in a vascular system of a living person. FIG. 1A is a longitudinal cross section of a normal healthy artery 10. The healthy artery 10 includes a main branch 12 which bifurcates into two smaller branches 14, 16. A lateral cross section of the healthy artery 10 is shown in Figure 1B. The healthy artery 10 is formed of three distinct layers. An inner layer 18 (or intima) of the artery 10 consists of a layer of elastic tissue on whose inner surface rests a layer of plate-like endothelial cells. A middle layer 20 (or media) of the artery 10 consists of smooth muscle cells. An outer layer 22 (or adventitia) consists of fibrous tissue. An arterial lumen 24 provides a conduit for blood flow. In a healthy artery 10 this lumen 24 is clear and unobstructed. In addition, the healthy artery 10 is highly elastic, dilating at each heart-beat as blood is driven into it.
FIG. 2A illustrates an arterial condition referred to as point stenoses, which could be caused by atherosclerosis. An atherosclerotic artery 26 is often characterized by obstructive tissue 28 (e.g. atheromous plaque) which forms in the lumen 24 of the artery 26. The obstructed segments 30, 32 of the artery 26 are referred to as stenotic segments and are characterized by a localized narrowing. In atherosclerosis, the obstructive tissue 28 is called plaque, and is typically formed of a fatty substance such as cholesterol. This obstructive tissue 28 builds up on the inner layer 20 of the atherosclerotic artery 26 and has an inelastic quality. The obstructive tissue 28 also tends to clog the lumen 24 of the artery 26 and impairs blood circulation.
As the obstructive tissue 28 in an atherosclerotic artery 26 grows larger, the lumen 24 of the artery 26 becomes smaller. In due course the lumen 24 of the artery 26 may be so narrowed that it becomes blocked. If this occurs in the coronary arteries the result is a coronary thrombosis, commonly known as a heart attack. If it occurs in the brain it causes a stroke. The cause of atherosclerosis is not known, but one factor is the consumption of excessive saturated fats. Another contributing factor in plaque development is believed to be the migration of smooth muscle cells (SMCs) across the vascular wall.
FIG. 3A illustrates another condition of the arteries known as hypertension. FIG. 3A is characterized by a generalized stenosis. Generalized stenotic arteries 34 are characterized by a generalized thickening of the arterial wall 138. The exact cause of this thickening is often unknown. Generalized stenosis of the arteries 34 is often associated with a decreased lumen 24 in the affected areas. The thickening of the arterial wall 138 can be due to a variety of factors including cells that grow larger in size (hypertrophic) cells, cells that multiply (proliferation), neoplasms, bacterial conglomerations, inflammatory cells, virally infected cells or other causes. The arterial wall 138 can have different characteristics depending on the factors responsible for the narrowing. In generalized stenotic arteries 34, the thickened arterial wall 138 can be elastic or inelastic depending on the nature of the underlying disease.
One well known medical procedure for diagnosing and treating certain diseases involves obtaining a biopsy sample of the afflicted area. Medical devices for obtaining a biopsy of different body structures such as the heart, muscles, intestines, and the uterus are well known in the art. As an example, a medical instrument known in the art as a Schulz-Caves bioptome is an endomyocardial biopsy device for removing a biopsy sample from the heart. In general, even though biopsy instruments are well known in the art, there are no prior art biopsy instruments specifically adapted for obtaining biopsy samples from the inner surface of an artery.
Some medical instruments, such as atherocatheters, are designed to break-up and remove obstructive tissue from a stenotic segment of an artery. U.S. Pat. No. 5,011,490 to Fischell is representative of this type of instrument. Atherocatheters, however, are not specifically designed to retrieve a tissue sample other than obstructive tissue (e.g. atheroma). This is because atherocatheters are designed to remove obstructive tissue which is inelastic, and to avoid healthy arterial tissue, which is elastic. These devices will therefore not function to retrieve any tissue other than an inelastic obstruction occurring at a stenotic segment of an artery. In addition, any tissue retrieved is entrained in blood making it difficult to isolate.
The present invention recognizes that in some instances it may be desirable to obtain a sample of arterial tissue which is not a part of a point stenosis. This may be healthy arterial tissue or diseased arterial tissue located at a segment of the artery having generalized or localized narrowing. As an example, in the past it has not been possible to obtain samples of the fragile endothelial cell layer that lines the inner surface of the artery. (See for instance the article by Bauriedel et al., entitled "Migratory Activity of Human Smooth Muscle", Circulation February 1992:85:2:554-564). The present invention also recognizes that it is desirable to retrieve a biopsy sample which is undamaged, isolated from blood and in an optimal condition for examination.
Information gained from the study of such arterial tissue may be useful in determining the cause and treatment of various cardiovascular maladies. As an example, millions of people suffer from what is called essential hypertension. This hypertension is deemed essential because there is no known cause, let alone cure, for it. The current treatment for hypertension entails prescribing drugs that reduce blood volume or relax blood vessels. While these medicines help control hypertension, this treatment does not cure hypertension, nor shed any light on the underlying causes of high blood pressure.
There are many different forms of hypertension, and they are characterized by a wide variety of symptoms and physiological changes. Hypertension can be caused by or be the cause of narrowing in the arteries. This narrowing can be systemic and generalized as in pulmonary hypertension, or localized into a point stenoses as in a concentration of atheromous plaque. Viral, bacteriological, oncological and inflammatory causes have also been postulated as causes of arterial hypertension, but until now there has been no procedure to sample tissues from areas other than localized stenoses.
Much of the effort and technological development of catheter systems that constitute the prior art has been concerned with dilating or eliminating point stenoses. Any sampling function performed is an added bonus. The prior art devices are not designed primarily for the purpose of taking a biopsy, nor do they perform in any other than highly specific conditions, namely, arteries with point stenoses.
In view of these and other shortcomings of the prior art, it is an object of the present invention to provide a method and apparatus for obtaining a biopsy sample from the inner surface of an arterial wall at an arterial segment without a localized stenoses. It is a further object of the present invention to provide a method and apparatus for obtaining a biopsy sample from the inner surface of an artery while minimizing trauma to the artery and to the biopsy sample.
It is yet another object of the present invention to provide a method and apparatus for obtaining a biopsy sample in which the orientation of the biopsy sample relative to the parent tissue is preserved. It is still another object of the present invention to provide a method and apparatus for obtaining a biopsy sample from an artery of a living being in which the risk of damage or puncture to the arterial wall is minimized.
It is a further object of the present invention to provide a method and apparatus for obtaining an endoarterial tissue sample that contains endothelial cells. It is a still further object of the present invention to provide a method and apparatus for obtaining a biopsy sample from an artery that includes one or more of the following constituents: smooth muscle cells, adventitia cells, thickened cells, hypertrophic cells, neoplastic tissue, bacterial conglomerations, virally infected cells, inflammatory cellular components, or cells containing exogeneously introduced recombinant genetical material.